Rosin is an abundantly available natural product. Rosin is mainly obtained from the exudation of pines and conifers. It is also obtained by the distillation of crude tall oil, which is a byproduct in the Kraft pulp process, or from aged pine stumps. Total world production of rosin is approximately 1.2 million tons annually. Rosin is a mixture of acidic (ca. 90%) and neutral (ca. 10%) compounds. The acidic components, generally named rosin (or resin) acids, are also a mixture containing mainly isomeric abietic-type acids (40-60%) and pimaric-type (9-27%) acids on the basis of total rosin weight. The exact composition of rosin acids varies, depending on the tree species and production location. Rosin and its derivatives have long been used as adhesive tackifiers, and are still mainly used in that market. In addition, rosin and its derivatives have also found other niche applications in printing inks, varnishes, paints, sealing wax, some soaps, paper sizing; soldering, plasters, etc.
In recent years, the drive for obtaining chemicals and materials from renewable resources has also prompted the research of new applications for rosin. Rosin acids, owing to their characteristic fused ring structure, are analogous to many aromatic compounds in rigidity. Therefore, rosin and its derivatives could become important alternatives to current fossil carbon-based aromatic monomer compounds in polymers.
In addition, epoxy adhesives are widely used in the aerospace, automatic, electronic and construction industries because of their outstanding mechanical properties, better wetting ability, good chemical and solvent resistance. However, the common epoxy resin are always rigid and brittle, which weakens their peeling properties and impact strength, and then limits their application field. To minimize the major shortcoming of this kind of adhesive, a number of techniques, such as flexibilizing the chemical structure of epoxy or incorporating modifiers into the adhesives, have been used.